Cyclodextrins are cyclic oligosaccharides containing six, seven, or eight (α-1,4)-linked D-glucopyranoside units resulting in alpha(α)-, beta(β)- and gamma(γ)-cyclodextrins. In general, cyclodextrins are pharmaceutical excipients that can solubilize various poorly soluble drugs/molecules through the formation of water-soluble drug-cyclodextrin complexes (Loftsson T et al., Journal of Pharmaceutical Sciences 2012, 101(9): 3019-3032). More specifically, cyclodextrins in aqueous solution form inclusion complexes with water-insoluble or poorly soluble drugs by taking up the lipophilic moiety of the drug molecule into the cavity of the cyclodextrin, which is hydrophobic (Brewster M E et al., Advanced Drug Delivery Reviews 2007, 59: 645-666). However, non-inclusion drug-cyclodextrin complexes can also be formed. The higher the cyclodextrin concentration increases, the higher the formation of aggregates of cyclodextrin molecules and self-assembled complexes. A further aspect with cyclodextrin containing pharmaceutical compositions is the formation of self-assembled complexes and/or formation of aggregates (Messner M et al., International Journal of Pharmaceutics 2011, 408: 235-247). Excipients that solubilize and stabilize such aggregates include small ionized molecules such as salts of organic acids and bases.
A substantial problem with pharmaceutical compositions including cyclodextrins is to produce pharmaceutical compositions which are preserved against microbial growth. Such preserved compositions are particularly important for storage of containers containing multiple-dose compositions. Typical preservatives are relatively ineffective at normal concentrations in such compositions, as compositions including such preservatives are unable to meet or pass standard preservative efficacy tests (for example USP <51> or Pharm. Eur. 5.1.3. It is believed that the preservative forms a complex with cyclodextrin and consequently is rendered ineffective or has reduced effectiveness as a preservative. Thus, the preservative loses its full activity by complex formation. The formation of these complexes between preservative and cyclodextrin further reduce the solubility of the active drug substance (Loftsson T et al., Drug Development and Industrial Pharmacy 1992, 18(13): 1477-1484).
Certain etherified β-cyclodextrin derivatives are known to improve solubility of sparingly soluble drugs, see WO 85/02767. However, in WO 85/02767 only the use of etherified β-cyclodextrin derivatives up to a concentration of 10% is described. A molar ratio of drug to etherified β-cyclodextrin derivative of 1:6 to 4:1 was contemplated. The solubility of flubendazol within the above given ratio was only increased by a factor 30. However, those formulations are not suitable for the preparation of pharmaceutical compositions comprising substituted benzimidazole derivatives, such as pimobendan.
Further prior art is as follows:
US 2004/152664 is directed to compositions comprising cyclodextrin derivatives and prednisolone.
WO 2004/089418 deals with a fluoroquinolone comprising aqueous formulations of a pH between 4 and 7.
EP 1 920 785 discloses a liquid preparation comprising a complex of pimobendan and cyclodextrin.
Brewster M E at al. (Advanced Drug Delivery Reviews 2007, 59(7): 645-666) describe cyclodextrins as pharmaceutical solubilizers.
Bassani V L et al. (Journal of Inclusion Phenomena and Molecular Recognition in Chemistry, 1996, 25(1-3): 149-152) refer to the enhanced water-solubility of albendazole by hydroxypropyl-β-cyclodextrin complexation.
The article of Piel G and co-workers (Sciences Techniques et Pratiques STP Pharma Pratiques 1999, 9(3): 257-260) is directed to the development of a parenteral and an oral formulation of albendazole with cyclodextrins.
This enables the development of a pharmaceutical composition for parenteral use but due to the reduced shelf-life of unpreserved compositions, it does not enable the development of a pharmaceutical multiple-dose composition for oral use. Due to the risk of severe tolerance problems and also due to concerns by pet-owners that inflammation in the subcutis following injections is considered to be a risk factor in the development of sarcomas, it is highly desirable to develop an oral pharmaceutical composition.
Due to some animals' intense sense of taste, it is particularly difficult to formulate a medication that can be administered orally and which the animal accepts resulting in an easy to use medication for animals, in particular companion animals, such as dogs, cats and horses (sufficiently good palatability).
The objective underlying the present invention is therefore to provide a pharmaceutical composition which overcomes the problems of the prior art as described above. Particularly, a pharmaceutical composition containing a sparingly water-soluble pharmaceutical active compound at palatable pH values (e.g. ≥pH 3) shall be provided to be administered in adequate form to a subject in need thereof.